Question

For making distinction between $2$-pentanone and $3$-pentanone the reagent to be employed is

• A. $K_{2} Cr_{2} O_{7} / H_{2} SO_{4}$
• B. $Zn-Hg / HCl$
• C. $SeO_{2}$
• D. Iodine/NaOH

Answer 1

Answer: (D)

Iodine/NaOH

Answer 2

Ketones having $CH_3CO$� group give yellow coloured iodoform with $I_2$ and $NaOH$.
$\underset{\text{2 - pentanone}}{CH_3CH_2CH_2\overset{\underset{||}{O}}{C}CH_3} + I_2 + NaOH \to$
$\underset{\text{iodoform}}{CHI_3} + CH_3CH_2CH_2COONa + NaI + H_2O$
$CH_3CH_2\overset{\underset{||}{O}}{C}CH_2H_3 + I_3 + NaOH \to$ No reaction
$\therefore I_2 /NaOh$ is used to distinguish betweenn $2$- pentanone and $3$- pentanone